Slugs or bullets fired from shotguns fitted with rifled barrels or from muzzleloaders are often fitted with a sabot that releases the slug or bullet as the projectile exits the muzzle of the firearm. Sabots significantly improve the range and accuracy of the projectile by engaging the rifling of the barrel to impart spin to the projectile and also seal the barrel around the projectile to prevent leakage of the generated propellant gasses around the projectile. Sabots for small arms, such as shotgun slugs or for muzzleloaders, typically comprise a plurality of wings extending from a base portion configured as a projectile seating base on which the projectile is seated. Prior to firing, the wings are folded forwardly to form a recess configured as a cup for receiving the projectile. As the saboted projectile travels down the barrel during firing, the wings and/or projectile seating base engage the rifling of the barrel to impart spin to the projectile. Once the saboted projectile exits the muzzle, the wings flare open, flexing where they attach to the projectile seating base, to slow the sabot and release the projectile to travel on to the target.
Sabots used for conventional firearms are often injected molded as a single body in a simple manufacturing process that maintains a low cost per unit of ammunition. Polymers, such as high density polyethylene, provide favorable characteristics such as engagement of barrel rifling, absorption of shock peaks from the propellant, and gas sealing. However, an inherent drawback of polymer sabots is that the polymer can unevenly axially deform, disintegrate or destruct when subjected to the high pressure forces used to fire the projectile. In particular, the projectile seating base, which is intermediate or sandwiched between the projectile and the propellant charge, experiences the significant compression during firing often resulting in substantial deformation. Uneven axial deformation of the projectile seating base and other parts of the sabot can impart generate a wobble, yaw, precession, and/or nutation of the projectile particularly after the projectile leaves the barrel resulting in diminished accuracy. Such uneven deformation and disintegration is also believed to effect the uniform deployment of the wings after the sabot exits the muzzle. In addition, higher ambient temperatures have been observed to increase disintegration of sabots having discs further diminishing the accuracy of the projectile.
Efforts have been made to reinforce polymer sabots and improve performance and accuracy. Metal discs are disclosed in U.S. Pat. Nos. 4,574,703, 5,214,238 and 7,302,892, positioned rearwardly of or embedded within the projectile seating base of the sabot to reinforce the projectile seating base and provide an “area multiplier”. Typically such metal discs are made of steel. The added weight of the larger metal discs for reinforcing sabots, particularly steel discs, increases the overall weight of the saboted projectile, requiring more propulsion for providing the same muzzle velocity for the projectile. Moreover, the manufacture of sabots with discs such as shown in the '892 patent require more difficult and complicated molding techniques, for example, insertion of the metal disc in a mold cavity before injection of the polymer resin.
The deformation of sabots may be exaggerated with saboted projectiles used in muzzle loaded firearms where the saboted projectile is loaded flush against the propellant charge. Unlike shotgun cartridges where compressible plastic wadding is positioned against the rear of the saboted projectile, the saboted projectile is positioned directly against the propellant charge and can allow for even greater deformation of the projectile seating base.
In addition to projectile seating bases in sabots of shotgun slugs, other projectile seating bases can be improved to provide more controlled uniform axial compression and thereby more uniform force to the projectiles and better accuracy.
There is a need for cartridge configurations where disintegration of the sabot is minimized with minimal additional weight and minimal additional cost. There is a need for shotgun shells with saboted projectiles with enhanced performance including consistently improved accuracy even under elevated and varying operating temperatures.